In the prior art, for measuring a height of a liquid compared to a reference height, it is known to employ floats which float on the liquid to ascertain the level of the liquid in the container by determining the position of the float in the container. It is further known to use magnetically sensitive sensors for measuring the level of a liquid. From DE 101 56 479 A1, it is known to employ a rotatably borne lever arm with a float attached to an end of the lever arm and the rotatably borne end connected to a ring magnet. The lever arm also has a sensor, and when the lever is moved, the ring magnet is moved with it, altering the magnetic influence of the magnet on the sensor which brings about an output signal corresponding to the liquid level. The sensor is a programmable Hall effect sensor. From DE 199 35 652 A1 it is known to connect a magnet to the float and to provide a sensor outside of the float's path of movement. The sensor measures the change in direction of the field lines of a magnetic field generated by the magnet depending on the position of the magnet moved by the float. The position of the float can be reproduced electrically on a display. From DE 199 25 185 A1 it is known to provide a float which is rotatably borne around an axis of rotation, and to mount at the axis of rotation of the float a magnet opposite a magnetic field sensor disposed in the interior of a pipe. The sensor sends a signal dependent on the angular position of the float to an evaluation apparatus via an electric line.
Further, from U.S. Pat. No. 3,982,087, GB 1395 075 and DE 32 41 250 A1 measuring devices are known for measuring the level of a liquid in a container in which reed contacts are employed as magnetically sensitive sensors. Reed contacts have movable components, however, and are not particularly well suited for use in containers installed in vehicles; the vibrations which occur during travel can damage the reed contacts. In measuring devices which employ reed contacts, a range of reed contacts are used which are sealed off in a housing from the liquid. The level of the liquid is detected through the switching of a respective reed contact. The precision of the system therefore depends on the size of the reed contacts and the number thereof per section of the measurement path. With such liquid level measuring devices using reed contacts, a precision of 10 to 20 mm is typically obtained.